package java1;

import java.util.Scanner;

public class Sqrt {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		while (in.hasNext()){
			double x = in.nextDouble();
			double epsilon = 0.0001,a = 0;
			if (x < 0)
				System.out.println(Double.NaN);
			else {
				while((x-Math.pow(a, 2)) >= epsilon && Math.pow(a, 2) < x)
					a += 0.0001;
				System.out.printf("%.6f\n",a);
			}
		}
	}
}
